The analysis of neuronal mechanisms in waking and attentive subhuman primates in the most direct method available for studying the physiological basis of human visual capacities. The objectives of the research described in this proposal are to identify and characterize the extent, distribution and functional properties of stereoscopic neurons in the cerebral cortex of rhesus monkey's and to understand how single neurons or sets of neurons process binocular information known to be relevant to the perception of depth. Experiments will be conducted in alert monkeys trained to maintain fixation of gaze. Stimuli will be presented stereoscopically, using a dual-screen, computer-controlled display system capable of generating line stereograms and random-dot stereograms. The position of both eyes will be monitored continuously in order to evaluate the extent of behavioral control on the monkey"s oculomotor activity. Three main studies will be conducted. First, experiments will be done to assess the response of neurons in striate cortex, at the earliest stages of binocular interaction, to random-dot stereograms, a powerful form of stimulation that tests the capacity of the visual system to identify the corresponding matches in binocular images and to extract out of the noise the disparity information leading to the perception of depth (global stereopsis). The available evidence suggests that striate neurons are capable of such processing. This study will explore the functional characteristics of these neurons, their distribution within the cortex, and will attempt to unravel the mechanisms of neuronal sensitivity to random-dot stereograms. A second series of experiments will address the question of where and how do cortical neurons signal binocular temporal disparity, how do these reponses interact with the neuron's responses to spatial disparity, and which are the mechanisms by which cortical neurons encode spatiotemporal binocular information. Finally, an attempt will be made to evaluate the influence of behavioral states, specifically attention and arousal, on the response properties of cortical visual neurons. The basic strategy for these experiments will be to train the monkey to attend to the very stimulus that activates the neuron under study and to identify differences in the neuron's responses when such stimulus is or is not behaviorally significant for the monkey.